Methods and devices for channel estimation

ABSTRACT

The present disclosure provides a method (100) in a network device for channel estimation. The method (100) includes: transmitting (110) to a terminal device an instruction to precode each of a number, L, of DeModulation Reference Signals, DMRSs, using a number, N, of linearly independent precoders, respectively; receiving (120) from the terminal device L*N precoded DMRSs; estimating (130) an equivalent channel associated with an uplink channel from the terminal device to the network device based on one or more of the L*N precoded DMRSs; and determining (140) the uplink channel from the equivalent channel based on the N precoders.

TECHNICAL FIELD

The present disclosure relates to wireless communication, and moreparticularly, to methods and devices for channel estimation.

BACKGROUND

Multiple Input Multiple Output (MIMO), particularly Multi-User MIMO(MU-MIMO) is a technique that can increase system throughput veryeffectively. Theoretically, when a number, M, of antennas are equippedat a network device (e.g., an evolved NodeB, or eNB), an M-layer MU-MIMOsystem can be supported or an increase of throughput by a factor of Mcan be achieved.

In order for a MIMO system to work properly, it is important that thenetwork device knows channels to/from all terminal devices (e.g., UserEquipments, or UEs) to be grouped. For example, an eNB can allocate aSounding Reference Signal (SRS) to a UE. Upon receiving the SRS from theUE, the eNB can estimate an uplink channel from the UE to the eNB basedon measurement of the SRS. In a Time Division Duplex (TDD) system, inaddition to the uplink channel, the eNB can obtain a downlink channelfrom the eNB to the UE due to channel reciprocity in TDD system.

SUMMARY

It is an object of the present disclosure to provide methods and devicesfor channel estimation.

According to a first aspect of the present disclosure, a method in anetwork device for channel estimation is provided. The method includes:transmitting to a terminal device an instruction to precode each of anumber, L, of DeModulation Reference Signals (DMRSs) using a number, N,of linearly independent precoders, respectively; receiving from theterminal device L*N precoded DMRSs; estimating an equivalent channelassociated with an uplink channel from the terminal device to thenetwork device based on one or more of the L*N precoded DMRSs; anddetermining the uplink channel from the equivalent channel based on theN precoders.

In an embodiment, the L*N precoded DMRSs can be received in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being received in one ofthe N TTIs.

In an embodiment, each of the L DMRSs can be used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L can be equal to 1 and the number N can be largerthan or equal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the equivalent channel can be a combination of theuplink channel and one of the N precoders, and the equivalent channelcan be estimated based on L of the L*N precoded DMRSs that are precodedusing the one precoder.

In an embodiment, the equivalent channel can be an average of Nequivalent channels each being a combination of the uplink channel andone of the N precoders, and the equivalent channel can be estimatedbased on L of the L*N precoded DMRSs that are precoded using the oneprecoder.

In an embodiment, the operation of determining can include: combiningthe N precoders into a precoding matrix; and deriving the uplink channelas a function of the equivalent channel and an inverse of the precodingmatrix.

In an embodiment, the instruction can include an indication of the Nprecoders and/or can be transmitted to the terminal device via DownlinkControl Information (DCI).

In an embodiment, the method can further include: determining a downlinkchannel from the network device to the terminal device based on theuplink channel.

According to a second aspect of the present disclosure, a network deviceis provided. The network device includes: a transmitting unit configuredto transmit to a terminal device an instruction to precode each of anumber, L, of DMRSs using a number, N, of linearly independentprecoders, respectively. The network device further includes: areceiving unit configured to receive from the terminal device L*Nprecoded DMRSs. The network device further includes an estimating unitconfigured to estimate an equivalent channel associated with an uplinkchannel from the terminal device to the network device based on one ormore of the L*N precoded DMRSs. The network device further includes adetermining unit configured to determine the uplink channel from theequivalent channel based on the N precoders.

According to a third aspect of the present disclosure, a network deviceis provided. The network device includes one or more processors and oneor more memories. The one or more memories contain instructionsexecutable by the processors, whereby the network device is operative toperform the method according to the above first aspect.

According to a fourth aspect of the present disclosure, a computerreadable storage medium is provided. The computer readable storagemedium has computer program instructions stored thereon. The computerprogram instructions, when executed by a processor in a network device,cause the network device to perform the method according to the abovefirst aspect.

According to a fifth aspect of the present disclosure, a method in aterminal device for facilitating channel estimation is provided. Themethod includes: receiving from a network device an instruction toprecode each of a number, L, of DMRSs using a number, N, of linearlyindependent precoders, respectively; and transmitting to the networkdevice L*N precoded DMRSs.

In an embodiment, the L*N precoded DMRSs can be transmitted in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being transmitted in oneof the N TTIs.

In an embodiment, each of the L DMRSs can be used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L is equal to 1 and the number N can be larger than orequal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the instruction can include an indication of the Nprecoders and/or can be received from the network device via DownlinkControl Information (DCI).

According to a sixth aspect of the present disclosure, a terminal deviceis provided. The terminal device includes a receiving unit configured toreceive from a network device an instruction to precode each of anumber, L, of DMRSs using a number, N, of linearly independentprecoders, respectively. The terminal device further includes atransmitting unit configured to transmit to the network device L*Nprecoded DMRSs.

According to a seventh aspect of the present disclosure, a terminaldevice is provided. The terminal device includes one or more processorsand one or more memories. The one or more memories contain instructionsexecutable by the processors, whereby the terminal device is operativeto perform the method according to the fifth aspect.

According to an eighth aspect of the present disclosure, a computerreadable storage medium is provided. The computer readable storagemedium has computer program instructions stored thereon. The computerprogram instructions, when executed by a processor in a terminal device,cause the terminal device to perform the method according to the fifthaspect.

According to a ninth aspect of the present disclosure, a communicationsystem is provided. The communication system includes a host computerincluding:

processing circuitry configured to provide user data; and acommunication interface configured to forward the user data to acellular network for transmission to a UE. The cellular network includesa base station having a radio interface and processing circuitry. Thebase station's processing circuitry is configured to perform the methodaccording to the first aspect.

In an embodiment, the communication system can further include the basestation.

In an embodiment, the communication system can further include the UE.The UE is configured to communicate with the base station.

In an embodiment, the processing circuitry of the host computer can beconfigured to execute a host application, thereby providing the userdata. The UE can include processing circuitry configured to execute aclient application associated with the host application.

According to a tenth aspect of the present disclosure, a method isprovided. The method is implemented in a communication system includinga host computer, a base station and a UE. The method includes: at thehost computer, providing user data; and at the host computer, initiatinga transmission carrying the user data to the UE via a cellular networkcomprising the base station. The base station can perform the methodaccording to the first aspect.

In an embodiment, the method further can include: at the base station,transmitting the user data.

In an embodiment, the user data can be provided at the host computer byexecuting a host application. The method can further include: at the UE,executing a client application associated with the host application.

According to an eleventh aspect of the present disclosure, acommunication system is provided. The communication system includes ahost computer including: processing circuitry configured to provide userdata; and a communication interface configured to forward user data to acellular network for transmission to a UE. The UE includes a radiointerface and processing circuitry.

The UE's processing circuitry is configured to perform the methodaccording to the fifth aspect.

In an embodiment, the communication system can further include the UE.

In an embodiment, the cellular network can further include a basestation configured to communicate with the UE.

In an embodiment, the processing circuitry of the host computer can beconfigured to execute a host application, thereby providing the userdata. The UE's processing circuitry can be configured to execute aclient application associated with the host application.

According to a twelfth aspect of the present disclosure, a method isprovided. The method is implemented in a communication system includinga host computer, a base station and a UE. The method includes: at thehost computer, providing user data; and at the host computer, initiatinga transmission carrying the user data to the UE via a cellular networkcomprising the base station. The UE can perform the method according tothe fifth aspect.

In an embodiment, the method can further include: at the UE, receivingthe user data from the base station.

According to a thirteenth aspect of the present disclosure, acommunication system is provided. The communication system includes ahost computer including: a communication interface configured to receiveuser data originating from a transmission from a UE to a base station.The UE includes a radio interface and processing circuitry. The UE'sprocessing circuitry is configured to: perform the method according tothe fifth aspect.

In an embodiment, the communication system can further include the UE.

In an embodiment, the communication system can further include the basestation. The base station can include a radio interface configured tocommunicate with the UE and a communication interface configured toforward to the host computer the user data carried by a transmissionfrom the UE to the base station.

In an embodiment, the processing circuitry of the host computer can beconfigured to execute a host application. The UE's processing circuitrycan be configured to execute a client application associated with thehost application, thereby providing the user data.

In an embodiment, the processing circuitry of the host computer can beconfigured to execute a host application, thereby providing requestdata. The UE's processing circuitry can be configured to execute aclient application associated with the host application, therebyproviding the user data in response to the request data.

According to a fourteenth aspect of the present disclosure, a method isprovided. The method is implemented in a communication system includinga host computer, a base station and a UE. The method includes: at thehost computer, receiving user data transmitted to the base station fromthe UE. The UE can perform the method according to the fifth aspect.

In an embodiment, the method can further include: at the UE, providingthe user data to the base station.

In an embodiment, the method can further include: at the UE, executing aclient application, thereby providing the user data to be transmitted;and at the host computer, executing a host application associated withthe client application.

In an embodiment, the method can further include: at the UE, executing aclient application; and at the UE, receiving input data to the clientapplication, the input data being provided at the host computer byexecuting a host application associated with the client application. Theuser data to be transmitted is provided by the client application inresponse to the input data.

According to a fifteenth aspect of the present disclosure, acommunication system is provided. The communication system includes ahost computer including a communication interface configured to receiveuser data originating from a transmission from a UE to a base station.The base station includes a radio interface and processing circuitry.The base station's processing circuitry is configured to perform themethod according to the first aspect.

In an embodiment, the communication system can further include the basestation.

In an embodiment, the communication system can further include the UE.The UE can be configured to communicate with the base station.

In an embodiment, the processing circuitry of the host computer can beconfigured to execute a host application; the UE can be configured toexecute a client application associated with the host application,thereby providing the user data to be received by the host computer.

According to a sixteenth aspect of the present disclosure, a method isprovided. The method is implemented in a communication system includinga host computer, a base station and a UE. The method includes: at thehost computer, receiving, from the base station, user data originatingfrom a transmission which the base station has received from the UE. Thebase station can perform the method according to the first aspect.

In an embodiment, the method can further include: at the base station,receiving the user data from the UE.

In an embodiment, the method can further include: at the base station,initiating a transmission of the received user data to the hostcomputer.

With the embodiments of the present disclosure, a network devicetransmits to a terminal device an instruction to precode each of L DMRSsusing N linearly independent precoders, respectively. Upon receivingfrom the terminal device L*N precoded DMRSs, the network deviceestimates an equivalent channel associated with an uplink channel fromthe terminal device to the network device based on one or more of theL*N precoded DMRSs and determines the uplink channel from the equivalentchannel based on the N precoders. In this way, the network device canobtain an estimate of the actual uplink channel, and possibly the actualdownlink channel, based on the precoded DMRSs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be moreapparent from the following description of embodiments with reference tothe figures, in which:

FIG. 1 is a flowchart illustrating a method in a network device forchannel estimation according to an embodiment of the present disclosure;

FIG. 2 is a flowchart illustrating a terminal device for facilitatingchannel estimation according to an embodiment of the present disclosure;

FIG. 3 is a block diagram of a network device according to an embodimentof the present disclosure;

FIG. 4 is a block diagram of a network device according to anotherembodiment of the present disclosure;

FIG. 5 is a block diagram of a terminal device according to anembodiment of the present disclosure;

FIG. 6 is a block diagram of a terminal device according to anotherembodiment of the present disclosure;

FIG. 7 schematically illustrates a telecommunication network connectedvia an intermediate network to a host computer;

FIG. 8 is a generalized block diagram of a host computer communicatingvia a base station with a user equipment over a partially wirelessconnection; and

FIGS. 9 to 12 are flowcharts illustrating methods implemented in acommunication system including a host computer, a base station and auser equipment.

DETAILED DESCRIPTION

As used herein, the term “wireless communication network” refers to anetwork following any suitable communication standards, such asLTE-Advanced (LTE-A), LTE, Wideband Code Division Multiple Access(WCDMA), High-Speed Packet Access (HSPA), and so on. Furthermore, thecommunications between a terminal device and a network device in thewireless communication network may be performed according to anysuitable generation communication protocols, including, but not limitedto, Global System for Mobile Communications (GSM), Universal MobileTelecommunications System (UMTS), Long Term Evolution (LTE), and/orother suitable 1G (the first generation), 2G (the second generation),2.5G, 2.75G, 3G (the third generation), 4G (the fourth generation),4.5G, 5G (the fifth generation) communication protocols, wireless localarea network (WLAN) standards, such as the IEEE 802.11 standards; and/orany other appropriate wireless communication standard, such as theWorldwide Interoperability for Microwave Access (WiMax), Bluetooth,and/or ZigBee standards, and/or any other protocols either currentlyknown or to be developed in the future.

The term “network device” refers to a device in a wireless communicationnetwork via which a terminal device accesses the network and receivesservices therefrom. The network device refers to a base station (BS), anaccess point (AP), or any other suitable device in the wirelesscommunication network. The BS may be, for example, a node B (NodeB orNB), an evolved NodeB (eNodeB or eNB), or gNB, a Remote Radio Unit(RRU), a radio header (RH), a remote radio head (RRH), a relay, a lowpower node such as a femto, a pico, and so forth. Yet further examplesof the network device may include multi-standard radio (MSR) radioequipment such as MSR BSs, network controllers such as radio networkcontrollers (RNCs) or base station controllers (BSCs), base transceiverstations (BTSs), transmission points, transmission nodes. Moregenerally, however, the network device may represent any suitable device(or group of devices) capable, configured, arranged, and/or operable toenable and/or provide a terminal device access to the wirelesscommunication network or to provide some service to a terminal devicethat has accessed the wireless communication network.

The term “terminal device” refers to any end device that can access awireless communication network and receive services therefrom. By way ofexample and not limitation, the terminal device refers to a mobileterminal, user equipment (UE), or other suitable devices. The UE may be,for example, a Subscriber Station (SS), a Portable Subscriber Station, aMobile Station (MS), or an Access Terminal (AT). The terminal device mayinclude, but not limited to, portable computers, image capture terminaldevices such as digital cameras, gaming terminal devices, music storageand playback appliances, a mobile phone, a cellular phone, a smartphone, voice over IP (VoIP) phones, wireless local loop phones, atablet, a wearable device, a personal digital assistant (PDA), portablecomputers, desktop computer, image capture terminal devices such asdigital cameras, gaming terminal devices, music storage and playbackappliances, wearable terminal devices, vehicle-mounted wireless terminaldevices, wireless endpoints, mobile stations, laptop-embedded equipment(LEE), laptop-mounted equipment (LME), USB dongles, smart devices,wireless customer-premises equipment (CPE) and the like. In thefollowing description, the terms “terminal device”, “terminal”, “userequipment” and “UE” may be used interchangeably. As one example, aterminal device may represent a UE configured for communication inaccordance with one or more communication standards promulgated by the3rd Generation Partnership Project (3GPP), such as 3GPP's GSM, UMTS,LTE, and/or 5G standards. As used herein, a “user equipment” or “UE” maynot necessarily have a “user” in the sense of a human user who ownsand/or operates the relevant device. In some embodiments, a terminaldevice may be configured to transmit and/or receive information withoutdirect human interaction. For instance, a terminal device may bedesigned to transmit information to a network on a predeterminedschedule, when triggered by an internal or external event, or inresponse to requests from the wireless communication network. Instead, aUE may represent a device that is intended for sale to, or operation by,a human user but that may not initially be associated with a specifichuman user.

The terminal device may support device-to-device (D2D) communication,for example by implementing a 3GPP standard for sidelink communication,and may in this case be referred to as a D2D communication device.

As yet another example, in an Internet of Things (IOT) scenario, aterminal device may represent a machine or other device that performsmonitoring and/or measurements, and transmits the results of suchmonitoring and/or measurements to another terminal device and/or networkequipment. The terminal device may in this case be a machine-to-machine(M2M) device, which may in a 3GPP context be referred to as amachine-type communication (MTC) device. As one particular example, theterminal device may be a UE implementing the 3GPP narrow band internetof things (NB-IoT) standard. Particular examples of such machines ordevices are sensors, metering devices such as power meters, industrialmachinery, or home or personal appliances, for example refrigerators,televisions, personal wearables such as watches etc. In other scenarios,a terminal device may represent a vehicle or other equipment that iscapable of monitoring and/or reporting on its operational status orother functions associated with its operation.

As used herein, a downlink, DL transmission refers to a transmissionfrom the network device to a terminal device, and an uplink, ULtransmission refers to a transmission in an opposite direction.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” and the like indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but it is not necessary that every embodiment includesthe particular feature, structure, or characteristic. Moreover, suchphrases are not necessarily referring to the same embodiment. Further,when a particular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to affect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

It shall be understood that although the terms “first” and “second” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed terms. The terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be liming of example embodiments. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises”, “comprising”, “has”,“having”, “includes” and/or “including”, when used herein, specify thepresence of stated features, elements, and/or components etc., but donot preclude the presence or addition of one or more other features,elements, components and/or combinations thereof.

In the following description and claims, unless defined otherwise, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skills in the art to which thisdisclosure belongs.

As discussed above, the channel estimation can be based on the SRS.However, the capacity of SRS is limited. In a typical Long TermEvolution (LTE) TDD configuration (TDD Configuration 2, Special SubframeConfiguration 7, Cyclic Shift 4, Comb 2), up to 32 UEs can each beallocated with an SRS every 10 ms. However, there may be quite many UEsin a cell, and this 32 SRS capacity may need be shared among hundreds ofUEs. In order to overcome the capacity issue of SRS, it is possible toestimate a channel by measuring an uplink DeModulation Reference Signal(DMRS). Thus, more UEs can be grouped using the MU-MIMO technique andthe system throughput can be improved.

If one single UE is equipped with more than one antenna, it is alsopossible to enable spatial multiplexing per UE to increase uplinkthroughput for the UE. Furthermore, codebook based solution has beenproposed for uplink transmission such that an eNB can control how layersare multiplexed for transmission. The DMRS transmitted from a UE to aneNB is also precoded according to a codebook configured by the eNB. Whenthe DMRS is precoded, the channel estimated based on the measurement ofthe DMRS would not be the actual channel and thus cannot be useddirectly e.g., to determine beamforming weights for MIMO transmissions.

FIG. 1 is a flowchart illustrating a method 100 for channel estimationaccording to an embodiment of the present disclosure. The method 100 canbe performed at a network device.

At block 110, the network device transmits to a terminal device aninstruction to precode each of a number, L, of DMRSs using a number, N,of linearly independent precoders, respectively. In an example, theinstruction can include an indication of the N precoders. Theinstruction can be transmitted to the terminal device via DownlinkControl Information (DCI), e.g., over Physical Downlink Control Channel(PDCCH).

Here, each of the L DMRSs can be used for one-layer transmission. L canbe smaller than a number of antennas at the terminal device and L*N canbe larger than or equal to the number of antennas at the terminaldevice. The number of antennas at the terminal device can be larger thanor equal to 2. In an embodiment, L can be equal to 1 and the number Ncan be larger than or equal to the number of antennas at the terminaldevice.

Preferably, the N linearly independent precoders can be orthogonal toeach other.

At block 120, the network device receives from the terminal device L*NDMRSs that are precoded using the N precoders, respectively. The L*Nprecoded DMRSs can be received in a relatively short time period withrespect to channel variation. Preferably, the L*N precoded DMRSs can bereceived in N consecutive TTIs or slots, with L precoded DMRSs that areprecoded using one of the N precoders being received in one of the NTTIs. Each TTI or slot can have a duration of e.g., 1 ms. Alternatively,the L*N precoded DMRSs can be received in N adjacent Physical ResourceBlocks (PRBs) in one TTI, with L precoded DMRSs that are precoded usingone of the N precoders being received in one of the N PRBs.

At block 130, the network device estimates an equivalent channelassociated with an uplink channel from the terminal device to thenetwork device based on one or more of the L*N precoded DMRSs.

In an example, the equivalent channel can be a combination of the uplinkchannel and one of the N precoders. The equivalent channel can beestimated based on L of the L*N precoded DMRSs that are precoded usingthe one precoder.

Alternatively, the equivalent channel can be an average of N equivalentchannels each being a combination of the uplink channel and one of the Nprecoders. The equivalent channel can be estimated based on L of the L*Nprecoded DMRSs that are precoded using the one precoder.

At block 140, the network device determines the uplink channel from theequivalent channel based on the N precoders.

In particular, in the block 140, the N precoders can be combined into aprecoding matrix and the uplink channel can be derived as a function ofthe equivalent channel and an inverse of the precoding matrix. It isassumed here that the uplink channel remains substantially constantduring the short time period (e.g., N consecutive TTIs).

In a TDD system, for example, a downlink channel from the network deviceto the terminal device can be determined based on the uplink channel, byutilizing the channel reciprocity.

The principle of the above method can be described mathematically asfollows.

It is assumed here that the network device is equipped with M antennasand the terminal device is equipped with N antennas, where M≥2, N≥2. Itis also assumed that L=1 and the number of precoders, and thus thenumber of precoded DMRSs, is N.

Let s denote the DMRS and an N-dimensional vector P_(i), i=1, 2, . . . ,N, denote the i-th precoder. The precoded DMRS can be represented as:d _(i) =P _(i) s,  (1)where d_(i) is an N-dimensional vector and denotes the i-th precodedDMRS that is precoded P_(i).

A signal received at the network device can be represented as:r _(i) =H _(i) d _(i) +n _(i) =H _(i) P _(i) s+n _(i),  (2)where r_(i) is an M-dimensional vector and denotes the signal receivedat the network device, H_(i) is an M*N matrix and denotes the uplinkchannel from the terminal device to the network device, and n_(i) is anN-dimensional vector and denotes a noise at the network device.

Let H′_(i)=H_(i)P_(i) denotes an equivalent channel, the above equation(3) can be rewritten as:r _(i) =H′ _(i) s+n _(i).  (3)

The equivalent channel H′_(i) can be estimated at the network device byusing any appropriate channel estimation technique.

The N precoders can be combined into a precoding matrix:P=[P ₁ P ₂ . . . P _(N)].  (3)

As discussed above, as the uplink channel typically remainssubstantially constant during a short time period (e.g., N consecutiveTTIs), i.e., assuming H₁=H₂= . . . H_(N), the uplink channel H_(i) canbe estimated as:H _(i) =H′ _(i) P ⁻¹.  (4)

Alternatively, an average of the N equivalent channels can be calculatedas:H′ _(avg)=(H′ ₁ +H′ ₂ + . . . H′ _(N))/N.  (5)

The uplink channel can be estimated as:H _(UL) =H′ _(avg) P ⁻¹.  (6)

Accordingly, when the channel reciprocity is applicable, the downlinkchannel can be calculated as:H _(DL) =H _(i) ^(T),  (7)orH _(DL) =H _(UL) ^(T),  (8)where ( )^(T) denotes transposition.

FIG. 2 is a flowchart illustrating a method 200 for facilitating channelestimation according to an embodiment of the present disclosure. Themethod 200 can be performed at a terminal device.

At block 210, the terminal device receives from a network device aninstruction to precode each of a number, L, of DMRSs using a number, N,of linearly independent precoders, respectively. In an example, theinstruction can include an indication of the N precoders. Theinstruction can be received via DCI, e.g., over PDCCH.

Here, each of the L DMRSs is used for one-layer transmission. L can besmaller than a number of antennas at the terminal device and L*N can belarger than or equal to the number of antennas at the terminal device.The number of antennas at the terminal device can be larger than orequal to 2. In an embodiment, L can be equal to 1 and the number N canbe larger than or equal to the number of antennas at the terminaldevice.

Preferably, the N linearly independent precoders can be orthogonal toeach other.

At block 220, the terminal devices transmits to the network device L*Nprecoded DMRSs. Here, the L*N precoded DMRSs can be transmitted in arelatively short time period with respect to channel variation.Preferably, the L*N precoded DMRSs can be transmitted in N consecutiveTTIs or slots, with L precoded DMRSs that are precoded using one of theN precoders being transmitted in one of the N TTIs. Alternatively, theL*N precoded DMRSs can be transmitted in N adjacent PRBs in one TTI,with L precoded DMRSs that are precoded using one of the N precodersbeing transmitted in one of the N PRBs.

Correspondingly to the method 100 as described above, a network deviceis provided. FIG. 3 is a block diagram of a network device 300 accordingto an embodiment of the present disclosure.

As shown in FIG. 3 , the network device 300 includes a transmitting unit310 configured to transmit to a terminal device an instruction toprecode each of a number, L, of DMRSs using a number, N, of linearlyindependent precoders, respectively. The network device 300 furtherincludes a receiving unit 320 configured to receive from the terminaldevice L*N precoded DMRSs. The network device 300 further includes anestimating unit 330 configured to estimate an equivalent channelassociated with an uplink channel from the terminal device to thenetwork device based on one or more of the L*N precoded DMRSs. Thenetwork device 300 further includes a determining unit 340 configured todetermine the uplink channel from the equivalent channel based on the Nprecoders.

In an embodiment, the L*N precoded DMRSs can be received in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being received in one ofthe N TTIs.

In an embodiment, each of the L DMRSs can be used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L can be equal to 1 and the number N can be largerthan or equal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the equivalent channel can be a combination of theuplink channel and one of the N precoders, and the equivalent channelcan be estimated based on L of the L*N precoded DMRSs that are precodedusing the one precoder.

In an embodiment, the equivalent channel can be an average of Nequivalent channels each being a combination of the uplink channel andone of the N precoders, and the equivalent channel can be estimatedbased on L of the L*N precoded DMRSs that are precoded using the oneprecoder.

In an embodiment, the determining unit 340 can be configured to combinethe N precoders into a precoding matrix; and derive the uplink channelas a function of the equivalent channel and an inverse of the precodingmatrix.

In an embodiment, the instruction can include an indication of the Nprecoders and can be transmitted to the terminal device via DownlinkControl Information (DCI).

In an embodiment, the determining unit 340 can further be configured todetermine a downlink channel from the network device to the terminaldevice based on the uplink channel.

The transmitting unit 310, the receiving unit 320, the estimating unit330 and the determining unit 340 can be implemented as a pure hardwaresolution or as a combination of software and hardware, e.g., by one ormore of: a processor or a micro-processor and adequate software andmemory for storing of the software, a Programmable Logic Device (PLD) orother electronic component(s) or processing circuitry configured toperform the actions described above, and illustrated, e.g., in FIG. 1 .

FIG. 4 is a block diagram of a network device 400 according to anotherembodiment of the present disclosure.

The network device 400 includes one or more processors 410 and one ormore memories 420. The memories 420 contain instructions executable bythe processors 410 whereby the network device 400 is operative toperform the actions, e.g., of the procedure described earlier inconjunction with FIG. 1 . Particularly, the memories 420 containinstructions executable by the processors 410 whereby the network device400 is operative to: transmit to a terminal device an instruction toprecode each of a number, L, of DMRSs using a number, N, of linearlyindependent precoders, respectively; receive from the terminal deviceL*N precoded DMRSs; estimate an equivalent channel associated with anuplink channel from the terminal device to the network device based onone or more of the L*N precoded DMRSs; and determine the uplink channelfrom the equivalent channel based on the N precoders.

In an embodiment, the L*N precoded DMRSs can be received in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being received in one ofthe N TTIs.

In an embodiment, each of the L DMRSs is used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L can be equal to 1 and the number N can be largerthan or equal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the equivalent channel can be a combination of theuplink channel and one of the N precoders, and the equivalent channelcan be estimated based on L of the L*N precoded DMRSs that are precodedusing the one precoder.

In an embodiment, the equivalent channel can be an average of Nequivalent channels each being a combination of the uplink channel andone of the N precoders, and the equivalent channel can be estimatedbased on L of the L*N precoded DMRSs that are precoded using the oneprecoder.

In an embodiment, the determining unit 340 can be configured to combinethe N precoders into a precoding matrix; and derive the uplink channelas a function of the equivalent channel and an inverse of the precodingmatrix.

In an embodiment, the instruction can include an indication of the Nprecoders and can be transmitted to the terminal device via DownlinkControl Information (DCI).

In an embodiment, the memories 420 can further contain instructionsexecutable by the processors 410 whereby the network device 400 isoperative to determine a downlink channel from the network device to theterminal device based on the uplink channel.

Correspondingly to the method 200 as described above, a terminal deviceis provided. FIG. 5 is a block diagram of a terminal device 500according to an embodiment of the present disclosure.

As shown in FIG. 5 , the terminal device 500 includes a receiving unit510 configured to receive from a network device an instruction toprecode each of a number, L, of DMRSs using a number, N, of linearlyindependent precoders, respectively. The terminal device 500 includes atransmitting unit 520 configured to transmit to the network device L*Nprecoded DMRSs.

In an embodiment, the L*N precoded DMRSs can be transmitted in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being transmitted in oneof the N TTIs.

In an embodiment, each of the L DMRSs can be used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L can be equal to 1 and the number N can be largerthan or equal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the instruction can include an indication of the Nprecoders and can be received from the network device via DownlinkControl Information (DCI).

The receiving unit 510 and the transmitting unit 520 can be implementedas a pure hardware solution or as a combination of software andhardware, e.g., by one or more of: a processor or a micro-processor andadequate software and memory for storing of the software, a ProgrammableLogic Device (PLD) or other electronic component(s) or processingcircuitry configured to perform the actions described above, andillustrated, e.g., in FIG. 2 .

FIG. 6 is a block diagram of a terminal device 600 according to anotherembodiment of the present disclosure.

The terminal device 600 includes one or more processors 610 and one ormore memories 620. The memories 620 contain instructions executable bythe processors 610 whereby the terminal device 600 is operative toperform the actions, e.g., of the procedure described earlier inconjunction with FIG. 2 . Particularly, the memories 620 containinstructions executable by the processors 610 whereby the terminaldevice 600 is operative to: receive from a network device an instructionto precode each of a number, L, of DMRSs using a number, N, of linearlyindependent precoders, respectively; and transmit to the network deviceL*N precoded DMRSs.

In an embodiment, the L*N precoded DMRSs can be transmitted in Nconsecutive Transmission Time Intervals (TTIs), with L precoded DMRSsthat are precoded using one of the N precoders being transmitted in oneof the N TTIs.

In an embodiment, each of the L DMRSs can be used for one-layertransmission, where L can be smaller than a number of antennas at theterminal device and L*N can be larger than or equal to the number ofantennas at the terminal device.

In an embodiment, the number of antennas at the terminal device can belarger than or equal to 2.

In an embodiment, L can be equal to 1 and the number N can be largerthan or equal to the number of antennas at the terminal device.

In an embodiment, the N precoders can be orthogonal to each other.

In an embodiment, the instruction can include an indication of the Nprecoders and can be received from the network device via DownlinkControl Information (DCI).

The present disclosure also provides at least one computer programproduct in the form of a non-volatile or volatile memory, e.g., anon-transitory computer readable storage medium, an ElectricallyErasable Programmable Read-Only Memory (EEPROM), a flash memory and ahard drive. The computer program product includes a computer program.The computer program includes: code/computer readable instructions,which when executed by the processors 410, cause the network device 400to perform the actions, e.g., of the procedure described earlier inconjunction with FIG. 1 ; or code/computer readable instructions, whichwhen executed by the processors 610, cause the terminal device 600 toperform the actions, e.g., of the procedure described earlier inconjunction with FIG. 2 .

The computer program product may be configured as a computer programcode structured in computer program modules. The computer programmodules could essentially perform the actions of the flow illustrated inFIG. 1 or 2 .

The processor may be a single CPU (Central processing unit), but couldalso comprise two or more processing units. For example, the processormay include general purpose microprocessors; instruction set processorsand/or related chips sets and/or special purpose microprocessors such asApplication Specific Integrated Circuit (ASICs). The processor may alsocomprise board memory for caching purposes. The computer program may becarried by a computer program product connected to the processor. Thecomputer program product may comprise a non-transitory computer readablestorage medium on which the computer program is stored. For example, thecomputer program product may be a flash memory, a Random-access memory(RAM), a Read-Only Memory (ROM), or an EEPROM, and the computer programmodules described above could in alternative embodiments be distributedon different computer program products in the form of memories.

With reference to FIG. 7 , in accordance with an embodiment, acommunication system includes a telecommunication network 710, such as a3GPP-type cellular network, which comprises an access network 711, suchas a radio access network, and a core network 714. The access network711 comprises a plurality of base stations 712 a, 712 b, 712 c, such asNBs, eNBs, gNBs or other types of wireless access points, each defininga corresponding coverage area 713 a, 713 b, 713 c. Each base station 712a, 712 b, 712 c is connectable to the core network 714 over a wired orwireless connection 715. A first user equipment (UE) 791 located incoverage area 713 c is configured to wirelessly connect to, or be pagedby, the corresponding base station 712 c. A second UE 792 in coveragearea 713 a is wirelessly connectable to the corresponding base station712 a. While a plurality of UEs 791, 792 are illustrated in thisexample, the disclosed embodiments are equally applicable to a situationwhere a sole UE is in the coverage area or where a sole UE is connectingto the corresponding base station 712.

The telecommunication network 710 is itself connected to a host computer730, which may be embodied in the hardware and/or software of astandalone server, a cloud-implemented server, a distributed server oras processing resources in a server farm. The host computer 730 may beunder the ownership or control of a service provider, or may be operatedby the service provider or on behalf of the service provider. Theconnections 721, 722 between the telecommunication network 710 and thehost computer 730 may extend directly from the core network 714 to thehost computer 730 or may go via an optional intermediate network 720.The intermediate network 720 may be one of, or a combination of morethan one of, a public, private or hosted network; the intermediatenetwork 720, if any, may be a backbone network or the Internet; inparticular, the intermediate network 720 may comprise two or moresub-networks (not shown).

The communication system of FIG. 7 as a whole enables connectivitybetween one of the connected UEs 791, 792 and the host computer 730. Theconnectivity may be described as an over-the-top (OTT) connection 750.The host computer 730 and the connected UEs 791, 792 are configured tocommunicate data and/or signaling via the OTT connection 750, using theaccess network 711, the core network 714, any intermediate network 720and possible further infrastructure (not shown) as intermediaries. TheOTT connection 750 may be transparent in the sense that theparticipating communication devices through which the OTT connection 750passes are unaware of routing of uplink and downlink communications. Forexample, a base station 712 may not or need not be informed about thepast routing of an incoming downlink communication with data originatingfrom a host computer 730 to be forwarded (e.g., handed over) to aconnected UE 791. Similarly, the base station 712 need not be aware ofthe future routing of an outgoing uplink communication originating fromthe UE 791 towards the host computer 730.

Example implementations, in accordance with an embodiment, of the UE,base station and host computer discussed in the preceding paragraphswill now be described with reference to FIG. 8 . In a communicationsystem 800, a host computer 810 comprises hardware 815 including acommunication interface 816 configured to set up and maintain a wired orwireless connection with an interface of a different communicationdevice of the communication system 800. The host computer 810 furthercomprises processing circuitry 818, which may have storage and/orprocessing capabilities. In particular, the processing circuitry 818 maycomprise one or more programmable processors, application-specificintegrated circuits, field programmable gate arrays or combinations ofthese (not shown) adapted to execute instructions. The host computer 810further comprises software 811, which is stored in or accessible by thehost computer 810 and executable by the processing circuitry 818. Thesoftware 811 includes a host application 812. The host application 812may be operable to provide a service to a remote user, such as a UE 830connecting via an OTT connection 850 terminating at the UE 830 and thehost computer 810. In providing the service to the remote user, the hostapplication 812 may provide user data which is transmitted using the OTTconnection 850.

The communication system 800 further includes a base station 820provided in a telecommunication system and comprising hardware 825enabling it to communicate with the host computer 810 and with the UE830. The hardware 825 may include a communication interface 826 forsetting up and maintaining a wired or wireless connection with aninterface of a different communication device of the communicationsystem 800, as well as a radio interface 827 for setting up andmaintaining at least a wireless connection 870 with a UE 830 located ina coverage area (not shown in FIG. 8 ) served by the base station 820.The communication interface 826 may be configured to facilitate aconnection 860 to the host computer 810. The connection 860 may bedirect or it may pass through a core network (not shown in FIG. 8 ) ofthe telecommunication system and/or through one or more intermediatenetworks outside the telecommunication system. In the embodiment shown,the hardware 825 of the base station 820 further includes processingcircuitry 828, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The base station 820 further has software 821 stored internally oraccessible via an external connection.

The communication system 800 further includes the UE 830 alreadyreferred to. Its hardware 835 may include a radio interface 837configured to set up and maintain a wireless connection 870 with a basestation serving a coverage area in which the UE 830 is currentlylocated. The hardware 835 of the UE 830 further includes processingcircuitry 838, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The UE 830 further comprises software 831, which is stored in oraccessible by the UE 830 and executable by the processing circuitry 838.The software 831 includes a client application 832. The clientapplication 832 may be operable to provide a service to a human ornon-human user via the UE 830, with the support of the host computer810. In the host computer 810, an executing host application 812 maycommunicate with the executing client application 832 via the OTTconnection 850 terminating at the UE 830 and the host computer 810. Inproviding the service to the user, the client application 832 mayreceive request data from the host application 812 and provide user datain response to the request data. The OTT connection 850 may transferboth the request data and the user data. The client application 832 mayinteract with the user to generate the user data that it provides.

It is noted that the host computer 810, base station 820 and UE 830illustrated in FIG. 8 may be identical to the host computer 730, one ofthe base stations 712 a, 712 b, 712 c and one of the UEs 791, 792 ofFIG. 7 , respectively. This is to say, the inner workings of theseentities may be as shown in FIG. 8 and independently, the surroundingnetwork topology may be that of FIG. 7 .

In FIG. 8 , the OTT connection 850 has been drawn abstractly toillustrate the communication between the host computer 810 and the useequipment 830 via the base station 820, without explicit reference toany intermediary devices and the precise routing of messages via thesedevices. Network infrastructure may determine the routing, which it maybe configured to hide from the UE 830 or from the service provideroperating the host computer 810, or both. While the OTT connection 850is active, the network infrastructure may further take decisions bywhich it dynamically changes the routing (e.g., on the basis of loadbalancing consideration or reconfiguration of the network).

The wireless connection 870 between the UE 830 and the base station 820is in accordance with the teachings of the embodiments describedthroughout this disclosure. One or more of the various embodimentsimprove the performance of OTT services provided to the UE 830 using theOTT connection 850, in which the wireless connection 870 forms the lastsegment. More precisely, the teachings of these embodiments may improvethe data rate and thereby provide benefits such as reduced user waitingtime.

A measurement procedure may be provided for the purpose of monitoringdata rate, latency and other factors on which the one or moreembodiments improve. There may further be an optional networkfunctionality for reconfiguring the OTT connection 850 between the hostcomputer 810 and UE 830, in response to variations in the measurementresults. The measurement procedure and/or the network functionality forreconfiguring the OTT connection 850 may be implemented in the software811 of the host computer 810 or in the software 831 of the UE 830, orboth. In embodiments, sensors (not shown) may be deployed in or inassociation with communication devices through which the OTT connection850 passes; the sensors may participate in the measurement procedure bysupplying values of the monitored quantities exemplified above, orsupplying values of other physical quantities from which software 811,831 may compute or estimate the monitored quantities. The reconfiguringof the OTT connection 850 may include message format, retransmissionsettings, preferred routing etc.; the reconfiguring need not affect thebase station 820, and it may be unknown or imperceptible to the basestation 820. Such procedures and functionalities may be known andpracticed in the art. In certain embodiments, measurements may involveproprietary UE signaling facilitating the host computer's 810measurements of throughput, propagation times, latency and the like. Themeasurements may be implemented in that the software 811, 831 causesmessages to be transmitted, in particular empty or ‘dummy’ messages,using the OTT connection 850 while it monitors propagation times, errorsetc.

FIG. 9 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 7 and 8 . Forsimplicity of the present disclosure, only drawing references to FIG. 9will be included in this section. In a first step 910 of the method, thehost computer provides user data. In an optional substep 911 of thefirst step 910, the host computer provides the user data by executing ahost application. In a second step 920, the host computer initiates atransmission carrying the user data to the UE. In an optional third step930, the base station transmits to the UE the user data which wascarried in the transmission that the host computer initiated, inaccordance with the teachings of the embodiments described throughoutthis disclosure. In an optional fourth step 940, the UE executes aclient application associated with the host application executed by thehost computer.

FIG. 10 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 7 and 8 . Forsimplicity of the present disclosure, only drawing references to FIG. 10will be included in this section. In a first step 1010 of the method,the host computer provides user data. In an optional substep (not shown)the host computer provides the user data by executing a hostapplication. In a second step 1020, the host computer initiates atransmission carrying the user data to the UE. The transmission may passvia the base station, in accordance with the teachings of theembodiments described throughout this disclosure. In an optional thirdstep 1030, the UE receives the user data carried in the transmission.

FIG. 11 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 7 and 8 . Forsimplicity of the present disclosure, only drawing references to FIG. 11will be included in this section. In an optional first step 1110 of themethod, the UE receives input data provided by the host computer.Additionally or alternatively, in an optional second step 1120, the UEprovides user data. In an optional substep 1121 of the second step 1120,the UE provides the user data by executing a client application. In afurther optional substep 1111 of the first step 1110, the UE executes aclient application which provides the user data in reaction to thereceived input data provided by the host computer. In providing the userdata, the executed client application may further consider user inputreceived from the user. Regardless of the specific manner in which theuser data was provided, the UE initiates, in an optional third substep1130, transmission of the user data to the host computer. In a fourthstep 1140 of the method, the host computer receives the user datatransmitted from the UE, in accordance with the teachings of theembodiments described throughout this disclosure.

FIG. 12 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 7 and 8 . Forsimplicity of the present disclosure, only drawing references to FIG. 12will be included in this section. In an optional first step 1210 of themethod, in accordance with the teachings of the embodiments describedthroughout this disclosure, the base station receives user data from theUE. In an optional second step 1220, the base station initiatestransmission of the received user data to the host computer. In a thirdstep 1230, the host computer receives the user data carried in thetransmission initiated by the base station.

The disclosure has been described above with reference to embodimentsthereof. It should be understood that various modifications,alternations and additions can be made by those skilled in the artwithout departing from the spirits and scope of the disclosure.Therefore, the scope of the disclosure is not limited to the aboveparticular embodiments but only defined by the claims as attached.

The invention claimed is:
 1. A method in a network device for channelestimation, the method comprising: transmitting, to a terminal device,an instruction to precode each of a number, L, of DeModulation ReferenceSignals (DMRSs) using a number, N, of linearly independent precoders,respectively; receiving, from the terminal device, L*N precoded DMRSs;estimating an equivalent channel associated with an uplink channel fromthe terminal device to the network device based on one or more of theL*N precoded DMRSs; and determining the uplink channel from theequivalent channel based on the N precoders.
 2. The method of claim 1,wherein the L*N precoded DMRSs are received in N consecutiveTransmission Time Intervals (TTIs) with L precoded DMRSs that areprecoded using one of the N precoders being received in one of the NTTIs.
 3. The method of claim 1, wherein each of the L DMRSs is used forone-layer transmission, where L is smaller than a number of antennas atthe terminal device, and wherein L*N is larger than or equal to thenumber of antennas at the terminal device.
 4. The method of claim 3,wherein the number of antennas at the terminal device is larger than orequal to
 2. 5. The method of claim 3, wherein L is equal to 1 and thenumber N is larger than or equal to the number of antennas at theterminal device.
 6. The method of claim 1, wherein the N precoders areorthogonal to each other.
 7. The method of claim 1, wherein theequivalent channel is a combination of the uplink channel and one of theN precoders, and the equivalent channel is estimated based on L of theL*N precoded DMRSs that are precoded using the one precoder.
 8. Themethod of claim 1, wherein the equivalent channel is an average of Nequivalent channels each being a combination of the uplink channel andone of the N precoders, and the equivalent channel is estimated based onL of the L*N precoded DMRSs that are precoded using the one precoder. 9.The method of claim 1, wherein said determining comprises: combining theN precoders into a precoding matrix; and deriving the uplink channel asa function of the equivalent channel and an inverse of the precodingmatrix.
 10. The method of claim 1, wherein the instruction comprises anindication of the N precoders and/or is transmitted to the terminaldevice via Downlink Control Information (DCI).
 11. The method of claim1, further comprising: determining a downlink channel from the networkdevice to the terminal device based on the uplink channel.
 12. A methodin a terminal device for facilitating channel estimation, the methodcomprising: receiving, from a network device, an instruction to precodeeach of a number, L, of DeModulation Reference Signals (DMRSs) using anumber, N, of linearly independent precoders, respectively; andtransmitting to the network device L*N precoded DMRSs.
 13. The method ofclaim 12, wherein the L*N precoded DMRSs are transmitted in Nconsecutive Transmission Time Intervals (TTIs) with L precoded DMRSsthat are precoded using one of the N precoders being transmitted in oneof the N TTIs.
 14. The method of claim 12, wherein each of the L DMRSsis used for one-layer transmission, where L is smaller than a number ofantennas at the terminal device, and wherein L*N is larger than or equalto the number of antennas at the terminal device.
 15. The method ofclaim 14, wherein the number of antennas at the terminal device islarger than or equal to
 2. 16. The method of claim 14, wherein L isequal to 1 and the number N is larger than or equal to the number ofantennas at the terminal device.
 17. The method of claim 12, wherein theN precoders are orthogonal to each other.
 18. The method of claim 12,wherein the instruction comprises an indication of the N precodersand/or is received from the network device via Downlink ControlInformation (DCI).
 19. A terminal device comprising one or moreprocessors and one or more memories comprising instructions executableby the processors, whereby the terminal device is operative to: receive,from a network device, an instruction to precode each of a number, L, ofDeModulation Reference Signals (DMRSs) using a number, N, of linearlyindependent precoders, respectively; and transmit, to the networkdevice, L*N precoded DMRSs.
 20. The terminal device of claim 19, whereinthe L*N precoded DMRSs are transmitted in N consecutive TransmissionTime Intervals (TTIs) with L precoded DMRSs that are precoded using oneof the N precoders being transmitted in one of the N TTIs.